Motions of the Celestial
Sphere
Constellations
• Sky looks like a
dome with the star
painted on the inside.
• 88 constellations such
as Ursa Major, Orion,
etc.
• Asterisms are not
constellations for
example the Big
Dipper, the Teapot,
etc.
Descriptions of Celestial Sphere
• Zenith-directly overhead
• Meridian – imaginary line
running north & south
through the zenith
• Horizon – where the sky
appears to intersect the
ground.
• Altitude – height of a star
above horizon (degrees).
The sky appear like a dome overhead.
Descriptions of Celestial Sphere
Stars are not a same distances.
So, constellations are not real places.
• North Celestial Pole (NCP) –
extension of Earth’s rotation
axis onto the sky.
• South Celestial Pole - ditto
• Celestial Equator – extension
of Earth’s equator onto the sky.
• Ecliptic – apparent yearly path
of Sun.
Rising and Setting of the Stars
• The stars, sun, moon
and planets all appear
to rise in the east and
set in the west.
• Reflection of Earth’s
rotation from west to
east.
Local Rising and Setting
of the Stars
• We live on the side of
the Earth.
• NCP’s altitude equals
your latitude.
• Circumpolar stars
never rise or set but
circle the NCP
Our view of Celestial Sphere
• We live on the side of
the Earth.
• Sky appears tilted at
an angle equal to our
latitude.
• Stars appear to move
in arcs across the sky
that are not
perpendicular to
horizon.
Our view of Celestial Sphere
• The sky appears to rotate around NCP.
• Altitude of NCP is always equal to your latitude
on Earth's surface.
A space ship lands on an unknown planet.
The occupants notice that the stars never rise
or set but appear to move in circles parallel
to the horizon.
Where on the planet did the space ship land?
a) At the equator.
b) At 45 degrees latitude.
c) At one of the celestial poles.
d) Cannot be determine.
Atlanta has a latitude of about 33 north degrees.
The star Polaris is very close to the Celestial North Pole.
What is the altitude of Polaris when viewed from Atlanta?
a) 33 degrees
b) 45 degrees
c) 57 degrees
d) 90 degrees
This picture is a time exposure of the night sky showing star trails as the
stars appear to rotate around the NCP.
What is the name of the bright star near the center of the rock arch?
Where are the circumpolar stars?